1. Field of the Invention
The present invention relates to an optical semiconductor device that has a long operating wavelength and comprises an indium phosphide substrate.
2. Description of the Related Art
As is well known, lasers operating at long wavelengths, i.e. above 1.5 μm, are intended to be used for optical data transmission in the so-called C band (1530–1570 nm) and/or the so-called L band (1570–1610 nm).
These lasers have a vertical structure formed from a stack of semiconductor layers on a semiconductor substrate. In this stack there is an active layer, conventionally with single or multiple quantum wells separated by barrier layers, and interposed between two optical confinement layers.
The document with the title “Leading-edge optoelectronic device production using two-inch technology” Simes, R.; Capella, R. M.; Fernier, B.; Mayer, H. P.; in Conference Proceedings of 7th International Conference on indium phosphide and related materials, 9–13 May 1995, pages 10–13 thus discloses a direct-modulation laser operating at 1.55 μm and at 2.5 Gbit/s, constructed on a substrate of indium phosphide InP. The quantum-well layer is an alloy In0.8Ga0.2As0.77P0.23.
This type of laser is not suitable for high-temperature operation without thermal regulation. For example, for a temperature of 85° C., the characteristic temperature T0 referred to the threshold current Is, which is defined by the relation Is85° C.=Is25° C.·eΔT/To is limited to about 45° K. And the characteristic temperature T1 referred to the differential efficiency η, which is defined by the relation η85° C.=η25° C.·e−ΔT/T1, remains below 130° K.
The aim of the invention is to provide a semiconductor optical device (continuous or direct-modulation laser, continuous laser combined with an electro-absorption modulator, semiconductor optical amplifiers, etc.) whose operating wavelength is within the C band or even the L band (bands possibly broadened) and which displays thermal and/or optoelectronic performance that is optimized in particular with respect to the temperature behaviour of the characteristics and/or the power emitted and/or if applicable the high-rate modulation behaviour.